With the advent of very low loss, low dispersion transmission lines made from high temperature superconducting (HTS) materials, e.g., materials that are superconducting at a temperature on the order of 77K, an easily insertable microwave switch becomes an important adjunct component for high performance signal control circuits. Potential applications include switched delay line phase shifters and microwave signal distribution networks. Such a switch would be useful in coplanar waveguides, microstrip lines and a variety of other known transmission systems. A practical device is characterized by low on-state insertion loss, good isolation and switching times on the order of a microsecond for many control applications. Faster switches can be attained with Josephson junction, as disclosed by T. Van Duzer et al., Principles of Superconductive Devices and Circuits, New York: Elsevier, 1981, Chp. 5[4]or flux flow devices, as disclosed by J. S. Martens et al. "Novel applications of Tl-Ca-Ba-Cu-O thin films to active and passive high frequency devices," presented at the 1990 Int. Symp. on Supercond., Sendai, Japan, Nov. 6-9, 1990, and J. S. Martens et al.,"A model and equivalent circuit for a superconducting flux flow transistor," IEEE Trans. on Appl. Supercond., vol. 1: Jun 1991. However, both of these switch types suffer from poor isolation unless they include fairly complicated, and, therefore, expensive, circuitry.
Another known type of switch, semiconductor-based switches, are difficult to integrate with superconductor materials and have insertion losses typically on the order of 2 dB.